Textile material having a durable antistatic property and the fibers to be used for its purpose

ABSTRACT

ELECTRICALLY CONDUCTIVE FIBERS COMPOSED OF (1) A SUBSTRATE WHICH IS A FIBER OF SYNTHETIC ORGANIC POLYMER AND (2) A COATING ADHERED TO SAID SUBSTRATE, SAID COATING BEING OF AVERAGE THICKNESS OF 0.5 TO 15 MICRONS AND COMPRISING AMATRIX OF A HARDENED RESIN MIXTURE OF AN ACRYLONITRILE-BUTADIENE COPOLYMER AND A PHENOLIC RESIN COMPATIBLE WITH THE COPOLYMER, AND FINELY DIVIDED SILBER AND/OR CARBON DISPERSED IN SAID MATRIX. THE ELECTRICALLY CONDUCTIVE FIBERS HAVE A VERY DURABLE ELECTRIC CONDUCTIVITY AS WELL AS EXCELLENT FUNCTIONAL PROPERTIES OF NORMAL TEXTILE FIBERS.

United States Patent 3,669,736 TEXTILE MATERIAL HAVING A DURABLE ANTI- STATIC PROPERTY AND THE FIBERS TO BE USED FOR ITS PURPOSE Shigeru Fujiwara, Kenji Nagae, and Tomomi Okuhashi, Tokyo, Japan, assignors to Teijin Limited, Osaka, Japan No Drawing. Filed May 26, 1969, Ser. No. 827,931 Claims priority, application Japan, June 4, 1968, 43/37,735 Int. C]. 0081: 47/12 US. Cl. 117-226 ABSTRACT OF THE DISCLOSURE Electrically conductive fibers composed of (1) a substrate which is a fiber of synthetic organic polymer and (2) a coating adhered to said substrate, said coating being of average thickness of 0.5 to 15 microns and comprising a matrix of a hardened resin mixture of an acrylonitrile-butadiene copolymer and a phenolic resin compatible with the copolymer, and finely divided silver and/or carbon dispersed in said matrix. The electrically conductive fibers have a very durable electric conductivity as well as excellent functional properties of normal textile fibers.

This invention relates to electrically conductive fibers having durable antistatic properties, to a process for making them and to textiles containing them.

Natural and man-made organic textile fibers generally have the drawback of becoming charged with static electricity when subjected to friction, especially at low humidity. This tendency is especially marked in the case of the hydrophobic fibres, for example of fully synthetic polymers such as polyamides, polyesters, polyacrylates, polyacrylonitrile and polyolefins and fibres of modified natural polymers such as cellulose acetate and triacetate fibres. This phenomenon causes problems not only in the use of textile materials containing these fibres but also in the production of such materials.

One method of solving these problems which has been proposed is to incorporate a small quantity of metallic fibres in the textile material (U.S. Pat. 3,288,175). However, in this method, it is necessary to use a metallic fibre having as small a denier as possible and even when a metallic fibre of fine denier is used problems still remain during the mixing and processing steps as Well as in the hand (i.e. feel) of the product, because normal textile fibres and metallic fibres are inherently incompatible. Moreover, since the manufacture of metallic fibres of fine denier is not simple and metallic fibres are expensive, this method is not a desirable one from the product quality and cost standpoints. It has also been proposed that electrostatic build-up can be prevented by incorporating, in ordinary textile fibers, electrically conductive fibers having carbon black dispersed therein (Japanese patent publication No. 4,196/ 1957; US. Pat. 2,845,962), but with the latter fibres, the desired conductivity cannot be ob tained unless substantial amounts of carbon black are dispersed throughout the fibre. In addition, the mechanical strength of such fibres is low and they tend to break during processing. As a result, the manufacture of antistatic textile materials and products according to this method is difficult. In addition, since it is necessary to use a relatively large proportion (at least 2% by weight) of this fibre, which is of course black, for achieving the antistatic effect, the appearance and hand of the product are not satisfactory.

Further, various electrically conductive paints or adhesives are also known; those comprising a conductive 5 Claims "ice material and, for example, an epoxy resin or acrylic resin, are commercially available, and are principally used in the manufacture of materials intended for electrical use, such as electrical terminals, printed circuits, resistors, heating elements and shielding materials. However, these latter paints are of no practical use in preparing textiles having a durably antistatic effect, because when they are applied to organic synthetic fibres having a denier (about 5 to 5 0) in the range used in textiles, the fibres so obtained, although initially of improved conductivity, do not retain this conductivity when subjected to the various conditions (for example friction, repeated flexing, repeated elongation and relaxation, scouring, dyeing and washing) to which textile fibres are subjected during their processing and use.

It has now been found that if an organic fibre is coated with a certain electrically conductive coating, the fibre so produced has a very durable conductivity as well as the functional properties of normal textile fibres. This conductive fibre can not only withstand the spinning, twisting, Weaving, knitting, sewing and heat treatments as well as scouring and dyeing, to which normal textile fibres are usually subjected, but surprisingly also possesses satisfactory durability to harsh crimp-imparting treatments such as gear-crimping and stuffer-box crimping. It has also been found that by mixing a small quantity of this conductive fibre with ordinary organic textile fibres, the undesirable tendency of the latter to build up a static charge can be very easily and semi-permanently controlled.

Thus, the invention provides an electrically conductive fibre composed of (1) a substrate which is a fibre of a synthetic organic polymer and (2) a coating adherent to the substrate, which coating is of average thickness 0.5 to 15 microns and comprises a matrix of a hardened mixture of an acrylonitrile-butadiene copolymer and a phenolic resin compatible with the copolymer, the weight ratio of the copolymer to the resin being 0.4:1 to 4:1, which matrix has dispersed therein finely divided electrically conducting material which comprises one or both of silver and carbon in an amount suflicient to lower the resistivity of the fibre to less than 10 ohm/cm.

The invention also provides textile materials having durable antistatic properties, which comprise organic textile fibres and a small quantity of electrically conductive fibres as defined above.

The term fibre, as used in this specification, refers, unless otherwise specified, to both staple and continuous fibres.

Preferably, the organic synthetic fibres to be used as said substrate are made from linear synthetic polyamides, especialy polycaproamide and polyhexamethylene adipamide, because of the mechanical strength of the fibres made therefrom and the adhesivenes's between these fibres and the conductive coating. However, other synthetic polymers, for example polyesters, polyolefins, acrylic polymers, polyvinyl acetals, polyureas and polyimide and the blends thereof can be used.

Suitably the fibres mentioned above are of about 5 to 50, preferably about 10 to 30, denier. Although the fibre used as starting material is preferably a monofilament, it may also be a multifilament if desired.

Silver and conductive carbon are selected as the conductive material in view of their weathering resistance, resistance to attack by chemicals, and conductivity. However, a small quantity of finely divided particles of other metals such as aluminium and copper can be added, if desired. The finely divided silver can be of any form provided that its average particle size does not exceed 10, preferably 5, microns, but a flat flaky finely divided silver is suitable. The fiat flaky silver having an average particle size not exceeding 5 microns is particularly suitable and results in a product having excellent and lasting conductivity, even when the thickness of the conductive coating is extremely thin. The carbon can be finely divided graphite and electrically conductive carbon blacks such as acetylene carbon black, conductive furnace black and conductive channel black. Acetylene black is preferred because its graphite structure is relatively well developed and its conductivity is superior. The particle sizes of carbon blacks are normally determined depending upon the process for their production, and almost all carbon blacks have an average particle diameter of approximately 0.1 In the present invention, all of electrically conductive carbon blacks having such a normal average particle diameter are usable. The finely divided graphite that can be employed has an average particle diameter of 0.5/L or below, preferably 0.1 or below. In general, silver gives a product of greater'durability and better appearance than carbon, but the latter is economically more attractive.

The upper-limit of the amount of the conductive material that can be present in the coating is restricted by the practical requirements of the strength of the coating and the adhesiveness between the coating and the substrate. In general, the presence of silver in the coating in an amount exceeding 90% by weight or carbon in an amount exceeding 60% by weight is not desirable. The optimum proportion by weight of the conductive material in the coating will depend upon the kind of the conductive material, its size and shape, and the thickness of the coating. However, from the practical standpoint, an amount ranging from about 70% to 90%, particularly about 75% to 85%, by weight, is preferred when silver alone is used..

On the other hand, about 10% to 60%, particularly about 15% to 45%, by weight, is better when carbon is used on its own.

Preferably, the acrylonitrile-butadiene copolymer contains about 28% to 42% by weight of units derived from acrylonitrile. If the content of acrylonitrile is too small, it frequently happens that the product obtained does not have satisfactory durability to scouring, dyeing and washing. On the other hand the copolymers in which the acrylonitrile content is too great are not desirable since they are not easily managed (specifically, because of their poor solubility since, as hereinafter described, they are dissolved in a solvent and then applied to the fibre). These copolymers may also contain a small amount, such as less than by weight, of units derived from other comonomers having carboxyl groups in its molecule such as acrylic acid and methacrylic acid.

As the phenolic resin, any phenolic resin which is compatible with said copolymer can be used in this invention. The phenolic resin is usually derived from a phenol and an aldehyde. When a copolymer of relatively high acrylonitrile content is used, a normal phenol-formaldehyde condensation product can be employed, but generally the oilsoluble phenolic resins are preferred. Examples are phenolic resins modified with natural resins such as rosin or withnatural oils such as cashew nut shell oil, and the condensation products of formaldehyde and a phenol substituted with, for example, a tertiary butyl, tertiary amyl, phenyl or cyclohexyl group. The commercially available Durez 12687 and Durez 11098 (Durez Plastics & Chem, Inc.), G.E. Resin 12316 and GE. Resin 12393 (General Electric Co.), Synco 721 (Snyder Chemical Co.), SP-12 and SP-8014 (Schenectady Resins & Varnish Co.) and CKRA 1977 and BKR 2620 (Bakelite Co.) are suitable oil-soluble phenolic resins.

The weight ratio of the acrylonitrile-butadiene copolymer to the phenolic resin is critical for satisfactory strength, softness and flexibility in the coating, adhesiveness to the substrate, resistance to attack by chemicals and resistance to weathering, and hence the durability of the product, and must be 0.4:1 to 4:1, preferably 0.6 :1 to 3: 1. When the amount of the phenolic resin component in the coating is too small, the strength of the coating, its resistance to chemicals and adhesiveness to the substrate is inadequate, whereas when it is too great, the

softeness and flexibility of the coating becomes inferior and the conductive fibre tends to lose its conductivity after repeated stretching flexing or friction.

The acryonitrile-butadene copolymer and phenolic resin mixture can also contain a phenolic resin hardener, such as hexamethylene-tetramine, thickening agent, antiaging agent or other additives.

The thickness of the electrically conductive coating is governed by requirements related to its conductivity as a conductive fibre and to the functional properties (as a textile) of the fibre. While this thickness will be influenced by the particular conductive material present in the coating and its size, shape and quantity, it has been found that the desired conductivity could not be achieved when the average thickness was less than 0.5 micron. On the other hand, the upper average thickness, though influenced by the denier of the substrate fibre, must not exceed 15 microns, but is preferably 1 to 12 microns. An excessively thick coating impairs the functional properties of the product as a textile fibre. When silver alone is used as the conductive material, the average thickness is preferably not. more than 10 microns, and is particularly about 0.7 to 5 microns, whereas in the case of carbon alone, the thickness is suitably at least one micron, particularly about 2 to 12 microns.

The electrically conductive fibres can be made from the substrate fiber and a paste of the acrylonitrile-butadiene copolymer, the phenolic resin, the finely divided conductive material and a volatile solvent, which is preferably a ketone, such as methyl ethyl ketone or methyl isobutyl ketone, chlorinated hydrocarbon such as dichloroethane, ester such asethyl acetate, nitrated hydrocarbon such as nitromethane, or a mixture thereof or a mixture thereof with a diluent, such as toluene. Thickening agents, antioxidants and other additives as well as curing agents for the phenolic resins can be suitably added to this paste. The paste is applied to the substrate fibre by dipping, coating, spraying or any other suitable means. If necessary, the amount of paste on the substrate is controlled, for example by passing the fibre through a slit. The fibre is dried at, say, about to C., and then heated at, say, about 130 to 210 C., to harden the resin composition.

The electrically conductive fibres so produced usually have resistivity of about 10 to 10 ohm/cm. when silver alone is present and about 10 to 10 ohm/m. when silver alone is present and about 10 to 10 ohm/cm. in the case of carbon alone. When carbon black and sliver are both used, depending upon the ratio of the two components, the resistivity of the fibre can approach that of the case where silver alone has been used. This fibre retains its functional properties as a textile fibre and is able to stand up against the usual processing conditions that textile fibres undergo. Hence, its incorporation in the usual organic textile materials is simplified.

The textile materials having a durable antistaticity are composed of normal organic textile fibres and a small quantity of the aforesaid electrically conductive fibres, and they can have the desired antistaticity and the mechanical properties and appearance that are satisfactory for practical purposes even if only a small quantity, say less than 2%, preferably 0.001 to 1.5%, by weight, of the conductive fibre is present.

The mixing of the conductive fibre and the organic textile fibres can be carried out by mixed spinning, mixed twisting, mixed weaving, mixed knitting or any other optional technique. Further, the former need not necessarily be distributed evenly in the latter. Carpet yarns, weaving or knitting yarns, or sewing threads can be first mixed with the conductive fibre and then the tufting, weaving, knitting or sewing may be carried out with the mixture, ensuring that the conductive fibre is present at suitable intervals in the end product. For example, a shirt may be sewn with a polyester cloth using a sewing thread containing about 8% by weight of the conductive fibre. In this case, the end product shirt contains only a mere 0.02% by weight of the conductive fibre, but it still demonstrates very satisfactory antistaticity. On the other hand, when the end product is a skirt, the undesirable phenomenon of the skirt and underwear acting together and clinging to the human body is controlled to a marked degree by merely sewing a single line of a conductive fibre in the hemmed portion of the skirt. In this case, the content of the conductive fibre based on the total skirt can be as little as 0.005% by weight.

Although the mechanism by which the static electricity is suppressed is still not clear, it is thought to be principally related to effects based on the electrostatic induction, i.e., the electrostatic induction may either facilitate the accumulated static charges to dissipate by discharge or cause apparent neutralization of the charges. Further, it is also expected that the charges on the human body may leak to the ground through the conductive fibre, thus preventing the human body from being electrified.

The textile materials can be for example a staple blend, spun yarn, twisted yarn, tape woven fabric, knit fabric, non-woven fabric, sewed articles or carpet.

The invention is illustrated by the following examples, a number of which are comparative examples outside the scope of the invention. In the examples, parts and percentages are by weight.

EXAMPLES 1-7 These examples illustrate the preparation and properties of coated fibres. The composition and thickness of the coatings on the substrate fibres and the resistivity of the fibres, initially and after various tests, is summarized in Table I.

Details of the various materials, procedures and tests used in Examples 1-7 are as follows.

(1) SUBSTATE FIBER Examples 1, lA-D, 2, 2A-D, 4 Al-6 and 4 Bl- A denier polycaprolactam monofilament.

Examples 3A l-7 and 33 1-7 A denier polycaprolactam crimped monofilament.

Examples 5A and B A 20 denier polyester monofilament.

Example 6 A 10 denier polyhexamethylene adipamide monofilament.

Example 7 A 30-denier, S-filament polycaprolactam multifilament.

2 CONDUCTING MATERIAL The silver used was finely-divided flaky silver of average particle size 1.5 microns.

The carbon used was acetylene black.

(3) MATRIX (a) Hardened mixture of acrylonitrile-butadiene copolymer and a phenolic resin In Examples 1, 2, 3, 6 and 7 the acrylonitrile-butadiene copolymer contained 32% acrylonitrile. In Example 4 the copolymer contained 37% acrylonitrile. In Example 5 the copolymer was a carboxylic acrylonitrile-butadieneggpp mer containing 32% acrylonitrile and about 1 mol p cent carboxyl group.

The phenolic resin used in Examples 1, 2, 3, 4 and 7 was a mixture of a phenol-formaldehyde resin of the novolac type modified with cashew nut shell oil and a small quantity of hexamethylene tetramine. The phenolic resin used in Example 5 was a mixture of a p-tert.butyl phenol-formaldehyde resin of the novolac type and a small amount of hexamethylene tetramine. The phenolic resin used in Example 6 was a mixture of a resorcinol-formaldehyde resin and a small amount of hexamethylene tetramine.

The column headed percent NBR in Table I shows the percentage by weight of copolymer, based on the total of copolymer and phenolic resin, for those examples in which such a mixture provided the matrix.

(b) Others The other resins used (for comparative purposes) to provide the matrix are designated by abbreviations in Table I below and are fully identified as follows:

Epan epoxy resin type adhesive (P 107-EC produced by Tokuriki Kagaku Kenkyujo, Japan); this suffered from the particular disadvantage that the pot life of the paste containing it was extremely short, thus making it difiicult to obtain a uniform coating, while the cure time required was long.

Ac-an acrylic resin type conductive paint (Dotite D-SOO produced by Fujikura Kasei Co. Ltd., Japan).

SiA silicone/ vinyl acetate (1 l) resin.

Pha phenol-formaldehyde resin of the novolac type modified with cashew nut shell oil.

(4) PRODUCTION OF COATED FIBRE A paste was prepared of the conducting material, the polymeric component(s) which, when hardened, forms the matrix, and a suitable volatile organic solvent. Thus in Example 1, parts silver, 12 parts acrylonitrile-butadiene copolymer, 8 parts phenolic resin and 80 parts methyl ethyl ketone were mixed; and in Example 2, 25 parts carbon, 45 parts acrylonitrile-butadiene copolymer, 30 parts phenolic resin and 350 parts methyl ethyl ketone were mixed.

The substrate filament (monofilament in Examples 1, 3, 4 and 6; a plurality of monofilaments separated from each other by a small distance, so that filaments do not stick to each other, in Examples 2 and 5, 30 filaments being processed together in Example 5; a multifilament in Example 7) was passed through the paste at a suitable speed (e.g. 25 metres/minute in Example 1) and then through a slit to adjust the thickness of the coating, and then subjected to a treatment to dry and harden the coating. The drying and hardening treatment used was as follows:

Examples 1, 2, 4, 5, 6 and 7 Fibres with acrylonitrile-butadiene copolymer/phenolic resin matrix: pass through a hot air C.) dryer for 6 seconds then through a hot air (200 C.) air bath for 6 seconds.

Fibres with another matrix: heat at 190 C.

Example 3 As for fibres with acrylonitrile-butadiene copolymer/ phenolic resin matrix in Examples 1 and 2, followed by heating of the filament wound up on a bobbin for 30 minutes in a hot air C.) air dryer.

(5) PROPERTIES OI? THE COATED FIBRES The resistivity of the coated fibre was measured [on an FM tester Model L-19-B' or an automatic insulation ohm meter Model L-68 (Yokogawa Electric Works, Japan)] 1i fter mpletion of the drying and hardening treatment,

and after the fibre had been subjected to all or some of a number of different tests, as follows:

Abrasion test The filament was rubbed for 15 minutes with a nylon gear (120 r.p.m., diameter 5 cm., number of teeth 20) under a load of 0.36 g./den., calculated on the basis of the substrate fibre.

Elongation test The filament was stretched 5% in length and then allowed to return to its original length, this cycle being repeated 50 times.

Scouting and dyeing test The filament was subjected to several scouring treatments, each for 60 minutes at 95 C. in a scouring bath containing 1 g./litre of a non-ionic detergent and 0.3 g./litre of sodium carbonate.

Then, the filament was dyed with an acid dye by a 60 minute treatment at 95 C. in a dye bath containing the dye and 0.15 g./litre of a surfactant and 0.16 g./litre of ammonium sulphate and adjusted to a pH of 4.6-4.8 with acetic acid.

Washing test The filament was subjected to washing treatments, each for 30 minutes at 60 C. in a wash liquid containing 1 g./litre of a detergent and 2 g./litre of sodium carbonate.

Chemical resistance tests The filament was (a) immersed for 20 hours at room temperature in trichloroethylene, tetrachloroethylene, toluene, 10% sulphuric acid, 20% sodium hydroxide and 20% acetic acid; and (b) allowed to stand for 20 hours at room temperature in nitrogen oxide gas, hydrogen sul phide and sulphur dioxide.

Weathering test The filament was exposed for 300 hours in weathering apparatus (Xenon Weathering Meter, Toyo Rika Instruments Inc., Japan).

Referring now to Table I, this shows, for each fibre,

(i) the type of matrix, the column headed percent NBR showing the percentage of acrylonitrile-butadiene co-. polymer, based on the total of acrylonitrile-butadiene copolymer and phenolic resin;

(b) after the abrasion test (Ab) (c) after the elongation test (El) (d) after the scouring and dyeing test (Sc) Where, in the column headed E1 the resistivity is given as 00 (1), this means that the resistivity was infinitely greater after the fibre had been elongated only once.

The examples which are in accordance with the invention are marked with an asterisk In addition to the resistivities shown in Table I, the resistivity of the fibres of Examples 1 and 2 was measured after other tests given above, and the fibre found to retain a very satisfactorily low resistivity.

The fibre of Example 1 had a tenacity at break of 5.6 g./den., an elongation at break of 43% and an initial Youngs modulus of 30 g./den. (based on the denier of the substrate). Thus the fibre had a tenacity, softness and flexibility substantially the same as substrate. Electrically conductive filaments in Examples 2, 3, 4, 5, and 6 where the substrate fibre is a monofilament and that in Example 7 which has been derived from the multifilament substrate are alike in their tenacity, softness, and flexibility. The thickness of an electrically conductive coating of the conductive filament in Example 7 is expressed in an average thickness of a conductive resin adhering to the surface of each component filament in the substrate multifilament.

The results shown in Table I demonstrate that the fibres of the present invention are easily prepared and exhibit excellent durability of their low resistivity under the conditions to which textile fibres are normally subject, whereas this is not true of coated fibres outside the invention.

TABLE I Matrix Resistivity (ohm/em.) Ex. Percent Ag 0 Thickness No. NBR Other percent percent (micron) In. Ab. El. Sc.

2. 9 26 1, 000 80 3. 2 40 5, 100 w (1) 300 2. 8 36 5. 6X10 6 m w 3. 0 44 w w (1) w 2. 9 27 w (1) 4.0 3.4)(10 4. 5X10 5. 2X10 7 6. 8X10 4.2 3. 5X10 5. 0X10 7 (1) 1.0)(10 4. 0 3. 5X10 5 4. 0X10 9 m w 3. 5 4. 0X10 5 w w (1) w 3. 8 3. 5X10 5 1. 7X10 8 w 5. 4X10 5 3. 2 28 w m w 3. 2 29 1. 3X10 5 w m 3. l 29 1, 000 100 3. 1 21 46 1, 000 3. 0 23 53 900 60 2. 9 25 4 0X10 1 w 60 2. 9 27 w m 60 4. 5 2. 4X10 5 w w w 4. 1 2 6X10 6 3 5X10 8 9 0X10 B m 3. 8 2 6X10 5 4 8X10 5 5 2X10 7 7. 2X10 5 4. 2 3 0X10 5 4 5X10 5 2X10 7 6. 8X10 5 3. 7 3.1X10 4 7X10 4 0X10 7 5. 4X10 5 3.9 3. 5X10 6 8X10 m 5.4Xl0 5 2.3 3. 5X10 5 1 7X10 m 5. 4X10 5 m 3. 9 30 55 800 2. 9 27 50 1, 000 80 0.7 5. 0X10 7 5. 0X10 5. 2X10 B 5 0X10 7 1. 7 35 1, 200 1. 7 30 m m 5. 0X10 4 13 m 8 15BX10 3 150x10 3 30, 000x10 8 200x 10 I 4 500X10 3 800X10 3 52, 000x10 3 1,000X10 7 2 1, 000x10 a 1, 500x10 3 70, 000x10 3 1, 700x10 3 8 400x10 3 w w 200x10 3 2. 1 40 1, 500 2. 5 2. 0X10 4. 5X10 7. 0X10 7 1. 0X10 1 3.8 2. 5X10 4 5. 5X10 4 7. 5X10 5 7.-5X10 4 l. 5 31 800 50 (ii) the :precentage of silver or carbon, based on the I EXAMPLES 8-15 These examples illustrate the preparation and properties of textile materials containing conductive fibres according to the invention. The voltages given in the examples are static charge voltages measured on a collecting type po- 75 tentiometer Model K-325 (Kasuga Electric Co., Japan).

Example 8 The monofilament prepared in Example 1 was twisted together with a crimped non-conductive nylon yarn (2600 total denier/ 136 filaments) and to give a conductive nylon yarn which was incorporated into four tufted carpets by disposing a line of the conductive yarns among the nonconductive yarns at every third, sixth, ninth and. twelfth interval respectively. A tufted carpet employing only the nonconductive nylon yarn was made as a control. The carpets were then scoured, dyed and supplied with backings. A person wearing leather-soled shoes then walked over them at 25 C. and 16% relative humidity; the saturated electrification voltage of the persons body and the carpets are shown in Table II.

The high electrification voltage of the persons body after walking on the control carpet is to be noted; a severe electric shock was received when a grounded conductor such as metal was contacted with the carpet. However, in all other cases the electrification voltage of the body was very low, and no electric shock was felt.

Example 9 The multifilament yarn prepared in Example 2 was incorporated in a tow with polyvinyl chloride filaments, which tow was crimped and cut to 76 mm. length staple fibre. The crimped conductive fibre retained its conductivity to an adequate degree.

This staple fibre (70 parts) was blended with polypropylene staple fibre (30 parts), made into a web and then into several nonwoven carpets by the needle punch method. The content of the conductive fibre in the carpets was varied by adjusting the number of filaments in the conductive multifilament yarn incorporated into the tow. A person wearing leather-soled shoes walked over these carpets and a control carpet at 25 C. and 27% relative humidity; the voltages of the persons body in each case are shown in Table III. A very high electrification voltage was built up in the body with the control carpet and a severe shock was received when a grounded conductor such as metal touched the latter. In all the other cases, however, the voltage built up in the body was extremely low and no such shock was felt.

Table III Conductive fibre Voltage of human content (percent): body (volt) Example Nylon tufted carpets were made as in Example 1 from the filaments prepared in Examples 3 A4 and 3 B-4, incorporating the filaments at every third interval. The carpets were abraded with a reciprocating rotary polyvinyl chloride friction element (1 cm. wide; r.p.m.;

46 cycles/min; load 1 kg./cm. The voltages, measured TABLE IV Voltage (volt) after abrading for- Filament of Specimen No. 10 min. 30 min. 60 min.

EX. 3 A-4 800 820 800 Ex. 3 B-4 830 850 850 Example 11 Plain fabrics of polyester fibres were prepared, incorporating the filaments prepared in Examples 4 A 2-5 and 4 B 2-4, interwoven laterally at 2 cm. intervals. The conductive filament contents in the fabrics varied from 0.05 to 0.08% depending upon the thickness of the coating and its composition. After scouring, the fabrics were rubbed with a nylon fabric at 25 C. and 22% relative humidity until a saturated static charge had built up. A control fabric had an electrification voltage (measured 30 sec. after rubbing) of as high as 24,000 volts and produced a harsh discharge noise, whereas the fabrics containing the conductive filaments had electrification voltages of only 1500 to 2000 volts, and gave no such discharge noise. Thus, a fabric having a very excellent antistatic elfect could be obtained by incorporating there n a small amount of the conductive filament having a resistivity falling within the range normally possessed by a high electric resistance [5x10 ohm/cm. (Example 4 A4)].

Example 12 A 60 count sewing thread was made by twisting in a single line of the conductive monofilament prepared in Example I with a polyester multifilament, and was used to sew a shirt of tricot composed of polyester fibre (conductive monofilament content about 0.04%).

This shirt and a control shirt sewn with conventional sewing thread were washed for 5 minutes with a nonionic detergent in a home electric washer. A dressing-undressing electrification test was carried out at 25 C. and 25% relative humidity on these shirts by a person wearing a polyvinyl chloride fibre undershirt. The control shirt produced a harsh discharge noise when the shirt was removed; the shirt also clung to the persons body. As can be seen from Table V, the control shirt produced high electrification voltages on both the body and the shirt after the latters removal, the measurement being made on the back portion of the shirt. With the shirt containing the conductive filament, the electrification voltages of the persons body and the shirt were very low even though the amount incorporated was extremely small. The test was repeated after the shirts had been washed a number of times, as shown in Table V, which shows that the improved effect was not lost, thus demonstrating its excellent durablity.

The multifilament yarn prepared in Example 5 was cut into staple fibres, which were mixed in various proportions with polyacrylonitrile staple fibres (3 denier; 76 mm.) and the staple fibre masses were rubbed with an acrylic resin plate at 25 C. and 40% relative humidity until the electrification voltage was constant. The electrification voltages (measured 30 see. after rubbing) of the samples are shown in Table VI.

TABLE VI Electrification voltage (volt) of blended staple fibre with conductive fibre contents (percent) of-- Fibre of aste example Y r 0. 1. 0% 1. 5% 2% 5% A very excellent antistatic efiect was obtained by incorporation of only a small amount of the conductlve staple fibres.

' Example 14 TABLE VII Carpet Conductive electrififilament cation Incorporation of conductive filament in earcontent voltage pet (percent) (volt) Control 0 6, 000 Alternate 0. 38 1, 700 Every third interval 0. 19 8,000

Example 15 Twill fabric of polyethylene terephthalate/ cotton blend was prepared, incorporating the electrically conductive filaments obtained in Example 7 in the warp direction at intervals of 5 cm. Wor-k wears were sewn from the twill fabric and scoured.

Then a dressing-undressing electrification test was carried out at 24 C. 40% RH on this work wear and a work wear not containing electrically conductive filaments by a person wearing a woolen sweater worn underneath.

When the work wear containing no electrically conductive filaments was put 01f, it produced a violent sound of electric discharge, and the charged voltage of body reached as much as 1+ 10 kv. As a result, the persons body received a severe shock on contact with good conductors such as metals. On the other hand, in the case of work wear containing the electrically conductive filaments of this invention, such troubles could not be seen with a charged voltage on the body being only +0.2 kv.

What we claim is:

1. An electrically conductive fiber for imparting durable antistatic properties to an electrically non-conductive textile material, said electrically conductive fiber comprising (1) a substrate of an organic synthetic fiber of 550 denier, and

(2) an electrically conductive coating bonded thereto,

said coating comprising a hardened polymer matrix of an acrylonitrile-butadiene copolymer and a phenolic resin compatible with said copolymer in the weight ratio of from 0.421 to 4:1, said matrix having dispersed therein finely divided particles of one or both of silver and carbon, the average thickness of said coating being 0.5 to 15 microns, and the amount of said particles being suflicient to reduce the resistivity of said electrically conductive fiber to less than 10 ohms per centimeter.

2. The electrically conductive fiber according to claim 1, wherein the fiber is in the form of a continuous filament.

3. The electrically conductive fiber according to claim 1, wherein silver particles having an average particle size not greater than 5 microns are dispersed in said matrix in an amount of '70 to 90% by weight based on the weight of the coating, and the average thickness of the coating is 0.5 to 10 microns.

4. The electrically conductive fiber according to claim 1, wherein carbon particles having an average particle size not greater than 0.5 micron are dispersed in said matrix in an amount of 10 to by weight based on the weight of the coating, and the average thickness of the coating is 1 to 15 microns.

5.. The electrically conductive fiber according to claim 1, wherein the copolymer contains 28 to 42% by weight of units derived from acrylonitrile.

References Cited UNITED STATES PATENTS 2,631,189 3/1953 Sullivan et a1 1 17-160 X 2,993,816 7/1961 Blake 1l7226 3,040,210 6/ 1962 Charlton et a1. 3172 3,288,175 11/19 66 Val-k0 57-439 X 3,402,061 9/1968 Faria et al 117-1383 X RALPH S. KENDALL, Primary Examiner C. WESTON, Assistant Examiner US. Cl. X.R.

117138.8 E, 138.8 'F, 139.5 A 

